In general, an ideal coating composition for filling gaps in a semiconductor substrate must satisfy the following seven requirements: (1) the coating composition must completely fill holes having an aspect ratio (i.e. a ratio between the diameter and height of the holes) of 1 or higher and a diameter of 100 nm or less by spin coating, and flatten a substrate to a uniform thickness; (2) no air voids or cracks must be present in portions of the film filled into the holes; (3) the thickness of the film after coating must be maintained constant, regardless of the density of the holes in the substrate; (4) the flattened film must be dissolved at a constant dissolution rate in a developing solution until a desired thickness is reached; (5) the thickness of the film must remain unchanged by washing with isopropyl alcohol (IPA) at 60-70° C. after thermal curing; (6) the film must be highly resistant to plasma etching after thermal curing; and (7) residue must be rapidly removed by ashing without being left inside the holes.
Many attempts have been made to fill gaps in semiconductor substrates. For example, a process is known wherein silicon oxide is deposited by plasma-enhanced chemical vapor deposition (PECVD) and then the resulting oxide layer is removed by chemical mechanical polishing or etch-back until a desired thickness is reached. According to this process, however, defects, e.g., air voids or cracks, are formed within holes or trenches having a diameter of 100 nm or less upon deposition of the oxide. Atomic layer deposition (ALD) equipment must be employed to minimize the formation of defects upon deposition of the oxide. This apparatus is highly priced and makes the deposition of the oxide slow, resulting in low throughput.